1. Field of the Invention
The present invention relates in general to smelt spouts, and in particular to a low pressure drop mass flow design smelt spout.
2. Description of the Related Art
Smelt spouts are troughs which serve as a means of egress for pulping chemicals known as smelt from a recovery boiler. In general, the internals of a smelt spout are water cooled to ensure a reasonably long working life.
Modern recovery boilers utilize water cooled tube and membrane walls to serve as the furnace enclosure. Openings for the smelt to exit are created by bending tubes to form smelt openings. In turn, the spout is either attached to the wall at the opening or is inserted into the opening.
Water cooled spouts are classified in two categories; external and inserted. External smelt spouts fit flush against the tube wall outside of the boiler, and smelt must flow over the tube wall opening surface prior to entering the smelt spout. Inserted smelt spouts are inserted and fitted through the wall, thereby covering the tube wall opening and lessening smelt contact with tubes.
The smelt spouts are operated with either pressurized or vacuum water cooling systems. The vacuum system may afford some additional safety in that there is less potential for water leakage which can cause a smelt water reaction which may lead to an explosion. Since an inserted spout has a greater tendency to release water into the furnace if a failure occurs at the inlet end of the spout, it is desirable to operate an insertable type spout in the vacuum mode.
Most existing insertable spouts are of a similar design, and have multiple passes on the water side of the spout that results in relatively high water side pressure drop and creates pockets where non-condensable gases and steam can collect and impede water flow and cooling. The higher pressure drop also means that the spout, to be operated in the vacuum mode, must run at high vacuum, therefore reducing the boiling point of the cooling water and the margin between operating temperature and that which the coolant would otherwise boil.